Big Bang Nucleosynthesis: Cosmic Evolution and Reactions

This lecture covers the fundamental concepts of Big Bang nucleosynthesis (BBN) and its implications for the early universe. It begins with a review of the general picture of BBN, emphasizing the abundance of light elements formed during this period. The instructor discusses the equilibrium conditions and the finite reaction rates that affect the abundance of elements like hydrogen, helium, and deuterium. Saha's equation is introduced to explain the relationship between temperature and particle densities. The lecture also addresses the role of neutrinos and their decoupling from matter, which is crucial for understanding the thermal history of the universe. The instructor highlights the significance of the cosmic microwave background (CMB) as evidence of BBN and its connection to the observed elemental abundances. The discussion includes the baryon-to-photon ratio and its implications for the formation of elements. The lecture concludes with a focus on nuclear reactions and binding energies, providing a comprehensive overview of the processes that shaped the early universe.